feat(MdTableCell): add md-id prop (vuematerial#1584)

Author: Samuell1

src/components/MdTable/MdTableCell.vue

@@ -10,6 +10,7 @@
   export default {
     name: 'MdTableCell',
     props: {
+      mdId: [String, Number],
       mdLabel: String,
       mdNumeric: Boolean,
       mdTooltip: String,
@@ -44,6 +45,7 @@
     methods: {
       setCellData ($vm = this) {
         this.$set(this.MdTable.items, $vm.index, {
+          id: $vm.mdId,
           label: $vm.mdLabel,
           numeric: $vm.mdNumeric,
           tooltip: $vm.mdTooltip,

src/components/MdTable/MdTableHead.vue

@@ -1,5 +1,5 @@
 <template>
-  <th class="md-table-head" :class="headClasses" :style="headStyles" @click="changeSort">
+  <th class="md-table-head" :id="id" :class="headClasses" :style="headStyles" @click="changeSort">
     <div class="md-table-head-container" v-if="$slots.default">
       <div class="md-table-head-label">
         <slot />
@@ -30,6 +30,7 @@
     props: {
       mdNumeric: Boolean,
       numeric: Boolean,
+      id: [String, Number],
       label: String,
       tooltip: String,
       sortBy: String